1. Field of the Invention
The present invention relates to a power supply apparatus in an electric vehicle such as a motor driven scooter, or the like. More particularly the present invention relates to a power supply apparatus in an electric vehicle for stabilizing a voltage generated on a power supply line by an electric motor, preventing a battery from being overcharged, preventing an overvoltage from being generated, and protecting system components from an overvoltage, even when no electric power is supplied from the battery to a control means for controlling the energization of the electric motor or the battery is removed.
2. Description of Background Art
Motor driven scooters have an electric motor for rotating an axle, e.g., a permanent-magnet brushless motor, and a power supply apparatus for energizing the electric motor with electric power supplied from a battery. The power supply apparatus has a regenerating function to operate the electric motor as a generator and charge the battery with electric power generated thereby when the motor driven scooter is running by inertia or running downhill. The power supply apparatus also has a function to stabilize a voltage on a power supply line which supplies electric power to the electric motor.
Japanese patent Laid-open No. Hei 5-49101 discloses a vehicle power supply protection circuit for preventing a power supply device on a vehicle from being overloaded. The vehicle power supply protection circuit has a controller for controlling the supply of electric power to a load depending on a voltage across the terminals of a battery. Specifically, the voltage across the terminals of the battery, which is charged by regenerative power from a rotary machine operating as a starter, is monitored by a control circuit. If the voltage across the terminals of the battery exceeds a reference value, then the electric power from the battery is supplied via an inverter circuit to the load (such as in a refrigerator, or the like). If the voltage across the terminals of the battery is equal to or lower than the reference value, then the inverter circuit is de-energized to prevent the battery from being overly discharged.
On electric vehicles, there is a possibility for the battery to be removed or for a switch for supplying electric power from the battery to the electric motor to be turned off intentionally during long downhill driving. When the battery is removed or the switch is turned off, the voltage on the power supply line is not stabilized and increases, thus making it difficult to protect components (FETs, etc.) of the power supply apparatus.
In the vehicle power supply protection circuit disclosed in Japanese patent Laid-open No. Hei 5-49101, the control circuit is supplied with electric power from the battery at all times. The control circuit is not designed to prepare for the situation when the battery is removed or the switch is turned off. Therefore, it is difficult to solve the above problems even if the disclosed arrangement is applied to an electric vehicle.
There has been a demand for a power supply apparatus for an electric vehicle which is arranged to stabilize a voltage on a power supply line and prevent an overvoltage from being generated on the power supply line even when a battery on the electric vehicle is removed or the electric vehicle is driven with the switch turned off.